In the described three-dimensional shaping method, it is adopted to repeat a process of sintering for a position at which a processed article is expected to be formed by scanning with the use of an optical beam, after step of formation of the powder layer.
Although the three-dimensional shaping method is accompanied with the characteristics and advantages to the maximum extent in that various types of shapes are adaptable in a processed article, it is unavoidable that there often arises a case that a cross-sectional area in a horizontal direction or a mean diameter is equal to or less than a predetermined extent, a case that a shaping width is equal to or less than a predetermined extent, and a case that an undercut angle formed by an upper face and a lower inclined face at the edge is equal to or less than a predetermined extent.
In each of above-described cases, when a sintered region is irradiated with an optical beam, not only a previously expected sintered region is formed only on a powder layer which has already been formed, but also, as shown in FIG. 11(a), (b), it is unavoidable to often arise such a case that raised sintered portions are formed at an upper side from a region of the powder layer.
In the case that such raised sintered portion is formed, when a powder supplying blade travels in order to form a powder layer on a next layer on the upper side of each layer to which sintering is performed, the raised sintered portions will, as shown in FIG. 11 (a), inevitably result in an accident such that the raised sintered portions collide with the powder supplying blade and a sintered region which has already been provided is deformed.
Furthermore, as shown in FIG. 11(b), the powder supplying blade inevitably collides and stops.
In order to avoid the above-described problem, inevitably, in a stage before traveling of the powder supplying blade for forming a powder layer of the next step, it is necessary to cut the raised sintered portions entirely or partially by using a rotating tool.
In order to cope with each of the cases that has been described previously, a great amount of time and complicated know-how are necessary for clearly distinguishing in advance a region at which the raised sintered portion is formed and also for realizing cutting of the raised sintered portion prior to a step of forming a next powder layer.
Nevertheless, spending a great amount of time does not always lead to find out the raised sintered portions with certainty.
Furthermore, the know-how is based on accumulation of subjective experience at work sites, and no objective standard can be obtained from such know-how.
Taking account the above-described situation, it is impossible to find out conventional technologies for dealing with raised sintered portions are in dealing with possible formation of the raised sintered portions or the raised sintered portions which have already been formed.
For reference, Patent Document 1 explains a problem covering raised sintered portions on three-dimensional shaping and a method for dealing with the problem (Paragraphs [0006], [0009] and [0045]). However, Patent Document 1 recognizes the problem as a problem of degree of wettability in a stage that a powder layer is irradiated with an optical beam and also dealt with the problem by using metal powder greater in wettability. Therefore, unlike the present invention, no consideration or measures are given to the raised sintered portions in each of the previously described cases.
In Patent Document 2, abnormal drive load with the use of a blade for keeping uniform the surface of a powder layer or an optical method is employed to detect a raised portion due to an abnormal sintered portion (claim 3, claim 4). Then, the raised portion due to an abnormal sintered portion is removed, while repeating formation of a sintered layer or after all the sintered layers are completely formed (the paragraph of [Solution] in [Abstract] and claim 1).
However, where the drive load with use of the blade is employed to detect the raised portion due to an abnormal sintered portion, it is necessary to stop the drive of the blade. On the other hand, it is also quite difficult to detect the abnormal sintered portion perfectly by an optical method.
In Patent Document 3 as well, the abnormal protrusions are detected based on an increase in torque of a motor for driving a blade (Paragraph [0052] with regard to FIG. 6 and claim 4) or detected by using an optical method for checking the presence or absence of received light (Paragraphs [0061] to [0063] with regard to FIG. 15 and claim 5). However, as with Patent Document 2, Patent Document 3 also has unavoidable technological defects.